Subpopulations of human bronchial epithelial cells in culture respond heterogeneously to 12-O-tetradecanoylphorbol-13-acetate (TPA) and other modulators of differentiation.

A greater understanding of the processes involved in the control of proliferation and differentiation should provide insight into the mechanisms involved in carcinogenesis. Studies were undertaken to examine the effects of modulators of differentiation on the proliferation, colony forming efficiency (CFE), and cross-linked envelope (CLE) formation of human bronchial epithelial (HBE) cells in culture. Treatment for 24 h with a low concentration of TPA (0.1 ng/ml) induced a 2-fold increase in CLE but little inhibition of CFE, suggesting that these two endpoints might be occurring independently of one another. Continuous culture in a low concentration of TPA (0.1 ng/ml) arrested growth in greater than 99% of the cells, but after 10-14 days, a few colonies were observed that were resistant to TPA. This TPA resistant subpopulation occurred at a frequency of less than 0.1% of the cells seeded into cultures. Short term treatment (24 h) with fetal bovine serum (FBS; 1-8%) or calcium (0.5-2 mM) resulted in 2-4 fold increases in CLE with no significant change in CFE. Continuous treatment with FBS or calcium for up to 5 days produced similar results. These findings suggest that different subpopulations of cells exist within cultures of HBE cultures, perhaps at different states of maturation, and that these subpopulations respond differently to modulators of differentiation.